1. Field of the Invention
This invention relates to hydraulic valves generally, and specifically to valves having sealed armatures.
2. Description of the Related Art
Hydraulic valves of the type which would be suitable for use in automatic transmissions and the like have historically been plagued by failures related to contaminants present in the transmission fluid. These contaminants generally include small metal filings and particles, some of which are produced during manufacture of the transmission and some which are a result of wear which occurs during operation. These contaminants enter the valve together with the fluid, and therein they can cause untold damage through several different mechanisms.
The first mechanism by which contaminants may cause damage is directly through contact with the valve closing apparatus. This could be a needle and valve seat in a needle type valve or a ball and valve seat where a ball type valve is used. If contaminants are present when the closing apparatus moves towards contact with the valve seat, premature contact occurs between the closing apparatus, contaminant, and valve seat causing leakage. Further motion causes destructive friction to occur. Repetitive motion combined with destructive friction will lead to a gradual wearing of the valve seat and valve closing apparatus, further adding to the initial contamination problem and further leakage. Eventually either the valve seat or closing apparatus will become sufficiently deformed so as to prevent complete closing of the valve and the valve will fail.
A second mechanism by which contaminants cause damage is more dependent upon the electromagnetic design of the system, as well as the mechanical configuration. In a system where ferromagnetic particles such as iron filings are likely to be present, the particles are readily attracted to the magnetic field used to activate the hydraulic valve. In the typical case of a transmission valve which is immersed in hydraulic fluid, the valve will act like a magnetic filter, attracting and retaining the ferromagnetic particles within the valve structure. The second mechanism, magnetic attraction, can result in failure of the valve simply by an eventual clogging of the valve by the gradually accumulating ferromagnetic contaminants. Where the valve is closed by a magnetic rod or ball seating directly upon the valve seat, the first type of wear mechanism described above is only worsened by the continued attraction of the contaminants to the magnetic closing apparatus.
Prior art patents have attempted to overcome many of the difficulties introduced by naturally prevalent contaminants. This attempt has been motivated by product warranties which are continually being extended, necessitating components which have ever increasing life expectancies. Some examples of these attempts are illustrated in U.S. Pat. No. 4,711,269 to Sule, U.S. Pat. No. 4,585,176 to Kubach et al, and U.S. Pat. No. 4,312,380 to Leiber et al, the foregoing patents incorporated herein by reference.
U.S. Pat. No. 4,312,380 to Leiber et al disclose in FIG. 1 a sealed valve arrangement designed for application in an antilock braking system. In order to overcome infiltration problems, Leiber et al utilized a dual chamber to restrict flow of fluid containing ferromagnetic materials to the region occupied by the electromagnet. However, in so doing, they have only further complicated the problems of a standard valve and additionally created new problems.
First, the Leiber et al disclosure has not solved any problems associated with wear occurring at the valve seat. Second, the Leiber et al disclosure has introduced an additional fluid flow path, around auxiliary push rod 15. This additional fluid flow path is subject to the same problems associated with contaminants as the closing apparatus (i.e.- wear during motion and ferromagnetic attraction of contaminants). While the Leiber et al disclosure has addressed the problem and has attempted to isolate the electromagnet from exposure to the contaminants, the addition of the extra components present greater possibility for contamination associated difficulties than the original basic design, while costing substantially more to manufacture. Particularly, clearances required for proper movement of the auxiliary rod are rapidly lost during repetitive movement of the auxiliary rod. Eventually, after relatively few actuations, the auxiliary rod will jam, resulting in valve failure. Further, the seal formed between the actuator and diaphragm is far from hermetic, being of a pressure fit variety.
The electromagnetic valve in U.S. Pat. No. 4,585,176 is disclosed as having application in fuel injection systems. In this patent grant to Kubach et al, there is disclosed a ball and diaphragm combination which is utilized to control flow of fluid through the valve. In the Kubach disclosure, fluid passes through ports in the valve to pass from one side of the diaphragm to the opposite side, past the valve seat, and out of the valve. In this disclosure, there is no seal created by the ball and diaphragm combination, but rather the diaphragm is used to apply a return spring force to the ball when the electromagnet is not actuated. In this disclosure, the ball is a ferromagnetic ball which would only serve to attract and trap ferromagnetic particles which will then accelerate the wearing of the device.
U.S. Pat. No. 4,711,269 to Sule et al discloses a sealed type valve for use in hydraulic and pneumatic valves. Described therein are other prior art techniques for accomplishing sealing. The prior art described, as well as incorporated into the Sule disclosure, utilize a flexible sealing diaphragm. This same diaphragm acts as the closing apparatus for the valve. While this technique certainly prevents destruction of the valve due to contamination of the electromagnet by ferromagnetic contaminants in the fluid, the design suffers severely from the first type of wear associated with destructive friction occurring at the valve seat. This destructive friction occurs because the valve closing apparatus must be flexible in nature. The material which is flexible is by its very nature not as wear resistant as other less flexible materials. Additionally, the complexity of the seals and the increased problems associated with internal misalignment do not add to the desirability o this design.